diff --git a/core/lib/Drupal/Core/Entity/ContentEntityForm.php b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
index a07d17bd55..958e26b042 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityForm.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
@@ -55,7 +55,7 @@ class ContentEntityForm extends EntityForm implements ContentEntityFormInterface
    */
   public function __construct(EntityRepositoryInterface $entity_repository, EntityTypeBundleInfoInterface $entity_type_bundle_info = NULL, TimeInterface $time = NULL) {
     if ($entity_repository instanceof EntityManagerInterface) {
-      @trigger_error('Passing the entity.manager service to ContentEntityForm::__construct() is deprecated in Drupal 8.6.0 and will be removed before Drupal 9.0.0.', E_USER_DEPRECATED);
+      @trigger_error('Passing the entity.manager service to ContentEntityForm::__construct() is deprecated in Drupal 8.6.0 and will be removed before Drupal 9.0.0. Pass the entity.repository service instead. See https://www.drupal.org/node/2549139.', E_USER_DEPRECATED);
     }
     $this->entityRepository = $entity_repository;
     $this->entityTypeBundleInfo = $entity_type_bundle_info ?: \Drupal::service('entity_type.bundle.info');
diff --git a/core/tests/Drupal/Tests/Core/Entity/ContentEntityFormTest.php b/core/tests/Drupal/Tests/Core/Entity/ContentEntityFormTest.php
new file mode 100644
index 0000000000..d4f884575b
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Entity/ContentEntityFormTest.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Drupal\Tests\Core\Entity;
+
+use Drupal\Component\Datetime\TimeInterface;
+use Drupal\Core\Entity\ContentEntityForm;
+use Drupal\Core\Entity\EntityManagerInterface;
+use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Entity\ContentEntityForm
+ * @group Entity
+ */
+class ContentEntityFormTest extends UnitTestCase {
+
+  /**
+   * @group legacy
+   * @expectedDeprecation Passing the entity.manager service to ContentEntityForm::__construct() is deprecated in Drupal 8.6.0 and will be removed before Drupal 9.0.0. Pass the entity.repository service instead. See https://www.drupal.org/node/2549139.
+   */
+  public function testEntityManagerDeprecation() {
+    $entity_manager = $this->prophesize(EntityManagerInterface::class)->reveal();
+    $entity_type_bundle_info = $this->prophesize(EntityTypeBundleInfoInterface::class)->reveal();
+    $time = $this->prophesize(TimeInterface::class)->reveal();
+    new ContentEntityForm($entity_manager, $entity_type_bundle_info, $time);
+  }
+
+}